The Contribution of Animal Experiments to the Surgery of Replacement
IN introducing the lecturer the Society's Chairman, Professor Henry Barcroft, in the unavoidable absence of the President, Lord Halsbury, said: "Ladies and Gentlemen, it is my great privilege to introduce to you another in the series of very distinguished lecturers we have had the honour of hearing at the annual meetings to emphasize to us the opinion of everybody who believes in the value of animals for the progress of medical research and this year we are favoured with an acceptance from Professor Sir Michael Woodruff. Sir Michael graduated inMelbourne. Australia and was in the Australian Army Medical Corps during the last war and after the war he had an opportunity to become especially interested in the fundamental side of surgery and this took him to the Chair of Surgery in the University of Otago, New Zealand from 1953 to 1958. In 1957 he was appointed Professor of Surgical Science,UniversityofEdinburghand Surgeon, Edinburgh Royal Infirmary. In 1968 he became Director of the Nuffield Transplantation Surgery Unit, Edinburgh, and in that year a Fellow of the Royal Society. It is my privilege this evening to introduce him to you and to ask him to address you on the subject of "The Contribution of Animal Experiments to the Surgery of Replacement”.
The Contribution of Animal Experiments to the Surgery of Replacement
BY PROFESSOR SIR MICHAEL WOODRUFF
Some people die of generalized disease: others live to a ripe old age and appear simply to wear out, rather like Oliver Wendell Holmes' "Wonderful One-Hoss Shay": "That was built in such a logical way
It ran a hundred years to a day
For the wheels were just as strong as the thills
And the floor was just as strong as the sills,
And the panels just as strong as the floor,
And the whipple-trcc neither less nor more,
And the back-crossbar as strong as the fore,
And the spring and axle and hub encore."
And so in the end it simply disintegrated:
"All at once and nothing first
Just as bubbles do when they burst."
But many people, like more ordinary mechanical contrivances, break down because of the failure of some particular part.
This failure may result in little more than a certain amount of inconvenience, but it may, on the other hand, cause serious disability or, when a vital organ is affected, threaten the patient's life.
Sometimes the loss or failure of a part can be compensated for by some other part assuming an additional load, as for example when a person loses one kidney and the remaining healthy one gradually learns to do the work of two, or, in the special case of an endocrine gland, by the patient being given the appropriate hormone. In other cases the question arises of replacing the defective part by either a mechanical appliance or a transplant, though of course whether or not this is indicated will depend on the severity of the patient’s disability, the inconvenience and risk of the procedure, and the degree of benefit which can reasonably be expected.
Mechanical appliances include prostheses, which may be either removable or permanently built-in, and artificial organs. Removable prostheses such as dentures, spectacles and artificial limbs need not concern us here since animal experiments have played little or no part in their development, but we shall have to consider briefly built-in prostheses, which are used in orthopaedic surgery, for example, to fix fractures, or to replace the whole or part of the hip joint in patients crippled with osteoarthritis, and in vascular surgery to replace or bypass occluded arteries. We shall also have something to say about artificial organs. The two in regular use today, namely, the artificial kidney and the heart-lung machine, are large pieces of apparatus to which patients are connected temporarily, but it seems possible that an artificial heart which can be inserted permanently in place of a patients own heart, will become available in the course of the next decade.
Transplants are of three main kinds: auio-transplants, allotransplants (sometimes called homotransplants) and xenoiransplants (sometimes called heterotransplants).
Autotransplanls are pieces of tissue or organs transplanted from one part of the patient's body to another. Autotransplants of skin, cartilage, tendon and bone are widely used in plastic and orthopaedic surgery, and for a variety of technical reasons it is sometimes necessary to move organs from one place to another, but this type of robbing Peter to pay Peter is clearly not going to help the patient whose life is threatened by irreversible failure of some vital organ.
Allotransplants are transplants from some other person (or in animal experiments from one animal to another of the same species). As a general rule they survive for a few days or weeks but are then destroyed as the result of an immunological reaction which they evoke in the recipient by virtue of the fact that the tissues of the body possess antigens of a particular kind which differ in different individuals. Some allotransplants are therapeutically useful even though they do not survive for very long, either because they tide the patient over a temporary crisis, as in blood transfusion, or because, as in the case of bone transplants, they provide a scaffolding which facilitates repair by the patient's own tissue. In other cases success depends on the transplant not only surviving but maintaining a satisfactory level of functional activity: it is therefore fortunate that there are exceptions to the rule that allotransplants are rapidly destroyed, notably when the tissue transplanted is avascular like the cornea, when the donor and recipient are what is known as "histocompatible", and when the recipient's reaction to the transplant has been abolished or weakened by some immunosuppressive therapeutic procedure. Complete histocompatibility occurs when the donor and recipient are identical twins: with randomly chosen donors the degree of compatibility varies widely, depending on the genetic make-up of the individuals concerned. Tests have been developed for measuring the degree of compatibility of a patient and prospective donor prior to transplantation, and these are important because in a high-compatibility situation the level of immunosuppression required to prevent rejection of the graft, and with it the risk of complications, may be reduced.
No one, I imagine, seriously doubts the value of transplants of skin, bone and cornea, as currently used in plastic, orthopaedic and ophthalmic surgery, but since there is still considerable scepticism about the value of organ transplants let me give you some facts which. I think, speak for themselves.
Transplantation of the kidney, which is now 'an established surgical procedure, provides the only alternative to lifelong regular dialysis with the artificial kidney for patients with severe, irreversible renal failure, and since the number of new cases presenting each year who require one or other of these forms of treatment is about 40 per million of population per year, the demand is great. As in so many other areas of medicine we are unable to restore normal life expectancy to these patients, but many who would otherwise die within a month or two can now be given some years of active and happy life. Some of the reported results of renal transplantation are summarized in Table 1. The figures from the kidney transplant registry are based on results from many different clinics in many countries, and during the last four years 60% of the cases reported were from clinics in which the number of transplant operations per year was less than six: it is not surprising therefore, that the results from particular clinics with a relatively large experience, of which two examples are cited, are significantly better than the world average.
It is noteworthy that patient survival, where shown, exceeds graft survival. This is because when a transplant fails the patient can still be maintained with the artificial kidney. The number of patients salvaged in this way would be greater if more places were available for them.
The number of kidney transplant operations which have been performed, though probably somewhat greater than the number reported to the registry, which by March. 1971 amounted to only 3,645, is pitifully small in relation to the need. The limiting factor however, is not technical, but social, and arises from the fact that we are unable to obtain more than a small fraction of the healthy kidneys which are potentially available from patients dying suddenly from head injuries and various other causes.
The expected survival of kidney transplants from cadavers, though still less than that of kidneys from living related donors, is much higher than it was some years ago, largely because we can now maintain the patient by dialysis if, as often happens, the transplant does not function adequately for the first week or two after operation. The lack of comparable means of providing temporary support after transplantation of the liver or heart is one of the main factors limiting the success of these procedures at the present time.
You may wonder at my mentioning heart transplantation at all, because many of the results reported since Barnard performed the first human heart transplant operation almost four years ago have been so poor that the operation has been virtually abandoned, at least for the time being, in Britain, and also in many centres in the United States and other countries. The results obtained by Shumway and his colleagues in San Francisco, however, which are summarized in the table alongside the results of kidney transplantation, are incomparably better than the general average and suggest that the time is ripe for a reappraisal of the situation.
To what extent, and in what ways, have animal experiments helped to make possible the great achievements in the surgery of replacement of which I have given you such a brief synopsis? It would take too long to cover the whole field, so I propose to consider mainly transplantation: indeed even with this limitation it will not be possible to tell more than a part of the story. To present a balanced picture, however. I must first make some reference to the role of animal experiments in the development of built-in metal and plastic prostheses and artificial organs.
Many foreign materials, even when scrupulously sterilized, evoke a severe reaction in the body, and in consequence cannot be used for the construction of such things as plates for the fixation of fractures, artificial hip joints, or tubes to replace or bypass blocked arteries. But how does one establish the safety of a new material? Chemical analysis and tissue culture techniques provide an initial guide, but it would be dangerous and irresponsible to proceed to clinical trial without first testing the material in living animals. This is how Venables and his colleagues in 1937 sought to elucidate the factors which influence the reaction of bones to metals, and established the safety of a new alloy, called vitalium, which has been of great importance in orthopaedic surgery. This is how the first woven tubes for use as substitutes for arteries were tested: this is the essential control without which the spectacular improvement in the quality of these and other prostheses would not have occurred.
Let us turn now to artificial organs. The first attempts in 1913 by Abel, Rowntree and Turner to provide a substitute for the kidney failed because it proved impossible at the time to prevent the blood flowing through the machine from clotting. These trials, however, paved the way for the later development of an effective artificial kidney machine by Kolff when the anticoagulant heparin became available, and it is surely fortunate that the lessons which had to be learned were learned from experiments in animals and not patients. The heart-lung machine, which has made open-heart surgery possible and so given new fife to thousands of patients, we owe to the painstaking experimental work of John Gibbon in dogs, and neither this achievement, nor the modifications and refinements which have subsequently been introduced by Kirklin, then at the Mayo Clinic. Lillehei inMinneapolis.Melrose at Hammersmith, and many others, would have been possible without the use of animals.
In the field of transplantation animal experiments have been especially important in the following ways.
In the first place they have been used to establish the feasibility of different forms of transplantation and to solve the various technical problems which arise. In the* case of organ transplants an essential pre-requisite was the development of safe and effective methods of blood vessel anastomosis, which we owe to the experimental work of Alexis Carrel, Charles Guthrie and others, during the early years of the present century. This, however, was not the only barrier to be surmounted: particular organs pose special problems, and it is no accident that Shumway, whose remarkable results with human heart transplants I quoted earlier, had been studying heart transplantation in dogs for years before he, or for that matter Professor Barnard, attempted this procedure in man.
Secondly, animal experiments have provided conclusive proof of the fundamental difference in the behaviour of autografts and allografts, and of the immunological nature of allograft rejection.
The history of this discovery is instructive. It begins about the beginning of the 19th century when Baronio and Dieffenbach began experimental skin grafting in animals and so paved the way for the clinical development of free skin grafting by Reverdin and Oilier in France, Lawson in England, Thiersch and Wolfe in Germany, and others, which began about 1870.
At first surgeons used autografts and allografts indiscriminately, and something like half a century wasChemical analysis and tissue culture techniques provide an initial guide, but it would be dangerous and irresponsible to proceed to clinical trial without first testing the material in living animals. This is how Venables and his colleagues in 1937 sought to elucidate the factors which influence the reaction of bones to metals, and established the safety of a new alloy, called vitalium, which has been of great importance in orthopaedic surgery. This is how the first woven tubes for use as substitutes for arteries were tested: this is the essential control without which the spectacular improvement in the quality of these and other prostheses would not have occurred.
Let us turn now to artificial organs. The firstto elapse before it was generally realized that, while allografts take almost as readily as autografts, they are. as a rule, destroyed within a few weeks, whereas autografts, excluding loss from infection and technical errors, survive indefinitely.
It may seem strange that it took so long for the truth to become apparent, but at the time there was a high failure rate even with autografts, and many surgeons were further misled by the superficial resemblance between an epithelialized scar and a surviving graft. Indeed, despite the insight of careful observers like Schone and Lexer inGermany, and Holman. Padgett and Davis in the United States, the process of enlightenment would have taken much longer but for the fact that the same difference was demonstrated with transplants of a whole variety of tissues in animals by Leo Loeb, Alexis Carrel and other investigators.
As I have already mentioned, allograft rejection results from an immunological reaction evoked by antigens of a particular kind which differ in different individuals. Evidence pointing in this direction is to be found in the results of early experiments with tumour transplants which began with Paul Ehrlich and became a major interest of workers at the laboratories of the Imperial Cancer Research Fund prior to the outbreak of the First World War, but its significance was not realized at the time. Loeb, who studied transplants of normal tissues as well as tumours, concluded correctly that chemical differences between the tissues of one individual and those of another lie at the root of the matter, but he failed to realize the true nature of the differences he described. ASan Franciscosurgeon, Emil Holman, in the light of clinical observations in a patient who received skin allografts from three different donors, made an inspired guess which has turned out to be substantially correct: but it remained for a Scottish surgeon. Thomas Gibson, and an English biologist, Peter Medawar, brought together by the exigencies of the Second World War, to find the essential clue which makes an immunological explanation of allograft rejection plausible. They were concerned with a burned patient who received two sets of small skin allografts from the same donor, and they observed that the first set grafts began to break down after 15 days, whereas the second set grafts showed advanced breakdown after eight days. Of course this single instance of what has since been called "the second-set phenomenon” by itself proved nothing, but it stimulated Medawar to embark on a systematic study of the behaviour of skin allografts in rabbits, in the course of which he demonstrated conclusively that small single allografts survive longer than large ones but that, if a set of grafts of different sizes is transplanted at one operation from a single donor to a single recipient, the period of survival is virtually the same for all members of the set. Furthermore, second-set allografts transplanted from the same donor 12 days or longer after the first operation are destroyed more quickly than grafts of the first set, whereas second-set allografts from a different donor sometimes survive as long as the original grafts.
Medawar's findings have been confirmed and extended by many other investigators, and a great deal of collateral evidence has beenobtained which has not only removed all reasonable doubt about the immunological nature of allograft rejection but has gone far to elucidating the underlying immunological mechanisms. The development of highly inbred strains of mice and other small laboratory animals, members of which are genetically virtually identical apart from the fact that some are male and others female, has greatly facilitated this work and has opened the way to investigations concerning the nature and variety of the transplantation antigens and the laws which govern their inheritance. The knowledge thus gained is fundamental to our understanding of histocompatibility typing, which has become such a major pre-occupation of surgeons engaged in transplantation.
To return to our list, the third important way in which animal experiments have promoted advances in transplantation is by delineating the important exceptions which I mentioned earlier to the rule that allografts are rapidly destroyed, and by showing that allografts of supporting tissues such as bone may provide a useful scaffolding which facilitates repair by the recipient's own tissue despite the fact that the cells of the transplant do not survive.
Finally, animal experiments have played a crucial role in the development of immunosuppressive procedures which, with the exceptions already mentioned, are necessary to prevent allograft rejection.
Immunosuppression is of two main kinds: non-specific immunosuppression, brought about by procedures such as whole body X-irradiation or the administration of immunosuppressive drugs or antilymphocytic globulin, in which the capacity of the organism to react to antigens in general is reduced, and specific immunosuppression, in which the diminished responsiveness is limited to a single antigen or group of antigens, for example the particular transplantation antigens which happen to be possessed by the donor of an allograft but are lacking in the recipient.
Animal experiments are clearly necessary to establish the safety and efficacy of new agents which seem likely to possess immunosuppressive properties, and all the agents currently used in clinical organ transplantation have been tested in this way. To omit such a precaution would be completely unethical, if not illegal, but rather than attempting to discuss this in detail I would refer you to the Stephen Paget lecture of 1962 in which my former colleague, Sir Derrick Dunlop, discussed the whole question of the safety of drugs in an authoritative and inimitable way.
Specific immunosuppression is achieved by the administration of either antigen or antibody. Normally, antigen provokes an immunological response and administration of antibody results in what is termed passive immunization, but under certain conditions which relate to the physical form of the antigen or the type of antibody, the dose and route of administration, the age of the recipient, and the concomitant use of procedures which normally cause nonspecific immunosuppression, the recipient may instead become specifically unresponsive.
Both methods of inducing specific immunosuppression were discovered in experimental animals. Neither has yet been used successfully in human transplant recipients, though I think that success with one or both will be achieved in the not very distant future. This will be a great advance because it should then be possible to avoid the increased liability to infection and other complications to which patients on lifelong non-specific immunosuppression are subject. Already, however, if you will permit a brief digression, immunosuppression by administration of antibody has proved to be of great value in the prevention of haemolytic disease of the newborn.
It is a great honour. Mr. Chairman, to be invited to deliver the Stephen Paget Memorial Lecture, but in accepting such an invitation one assumes a great responsibility. For the task of the lecturer, as I see it, is not only to give a true account of research in some particular field, but to present the truth in such a way that it will make some impact even on those who feel constrained to close their ears, lest they should hear: their eyes, lest they should see. An almost impossible assignment, it would seem. But if, as Dryden put it, "A man is to be cheated into passion but to be reasoned into truth", it is an assignment one could not refuse. Acknowledgement
I am grateful to the editors of Transplantation and the World Kidney Transplant Registry, and to the editor of the Lancet for permission to reproduce the results of kidney transplantation in Table 1, lines 1-4 and line 5 respectively. I am grateful also to Dr. Norman Shumway for permission to cite his results with heart transplantation in the last line of the same table.
The Chairman called upon Professor H. D. Ritchie to pass a vote of thanks, which he did, paying a tribute from surgeons as well as from members of R.D.S.